One proposed configuration of the non-contact power transmitting/receiving system includes a wireless power transmission device and a wireless power receiving device (see, for example, JP 2014-183731A). In this system, when an electric power transmitted from the wireless power transmission device is smaller than a power required by the wireless power receiving device, a power increase request message is sent from the wireless power receiving device to the wireless power transmission device. When receiving the power increase request message, the wireless power transmission device increases the intensity of electric current flowing through a power transmitting coil and thereby increases the transmitted electric power. When an electric power that is larger than the required power which is required by the wireless power receiving device is transmitted from the wireless power transmission device, on the other hand, a power decrease request message is sent from the wireless power receiving device to the wireless power transmission device. When receiving the power decrease request message, the wireless power transmission device decreases the intensity of electric current flowing through the power transmitting coil and thereby decreases the transmitted electric power.